1. Field of the Invention
The present invention relates to a process for production of a solid catalyst containing antimony oxide as one of the effective components and suitable for use in fluidized bed reactions. More particularly, it is concerned with a process for production of a fluidized bed solid catalyst containing attrition resistant antimony oxide which does not contain extremely fine particles nor coarse particles unsuitable for practical use and whose particle diameter is controlled.
2. Description of the Prior Art
Antimony oxide-containing catalysts are useful for ammoxidation of olefins to the corresponding unsaturated nitriles, oxidation of olefins to the corresponding aldehydes, and oxidative dehydrogenation of olefins to the corresponding diolefins, and these catalysts are described for example, in U.S. Pat. Nos. 3,657,155, 3,686,138, 3,716,496 and 3,988,359. The above described reactions can be effected in either a fixed bed or a fluidized bed, but they are generally carried out in a fluidized bed with which it is easy to remove the reaction heat since the heat of reaction thereof is great. In this fluidized bed reaction, it is important, of course, for the activity and strength of the catalyst to be high for the reaction to effectively proceed by keeping the catalyst particles in a good fluidized state. It is also well known that a suitable particle size distribution is very important. The particle diameter of the catalysts used in this fluidized bed reaction is generally not more than 500 .mu. and the average particle diameter is generally in a range of about 40 .mu. to 200 .mu..
With regard to a process for production of an antimony oxide-containing fluidized bed catalyst, a method has been proposed comprising preparing a slurry containing an antimony compound, a polyvalent metal compound and a silica sol as essential components, adjusting the pH of the slurry, heat-treating the slurry, subjecting the slurry so treated to a spray-drying operation to form spherical particles, and calcining the resulting particles, as described in U.S. Pat. Nos. 3,657,155 and 3,686,138. In this process, a catalyst having the desired particle size distribution is produced by controlling the spray-drying conditions in subjecting the above slurry to the spray-drying operation. By such an operation, however, it is quite difficult to produce the objective catalyst having the desired particle size distribution.
That is, in accordance with the above process, unnecessary small catalyst particles are more or less produced inevitably. In a fluidized bed reaction, these small catalyst particles cause the problems in that they are quickly lost during the reaction, resulting in a reduction in the yield of the object product and in an increase in catalyst unit cost and in that the amount of waste solids increases, resulting in the formation of pollution problems. On the other hand, if the above described spray-drying conditions are controlled to produce those catalyst particles having larger particle diameters so that the above described problems are eliminated, those catalyst particles having a particle size distribution in which coarse particle are predominent, are produced, and thus problems occur in that the fluidizability of the particles deteriorates and good results are not obtained.
The problem arises in the fluidized bed reaction that even though catalyst particles having a suitable size distribution are employed, those catalyst particles having a small diameter are inevitably scattered and lost, and thus the proper particle size distribution is destroyed and those catalyst particles having greater diameters become predominent. In this case, it is necessary to produce make-up catalyst particles having smaller diameters so that the proper particle size distribution is maintained. In producing catalysts with appropriate particle diameters for make-up, however, it is quite difficult to obtain a catalyst of the desired particle size distribution only by controlling the above described spray-drying conditions.
Under these circumstances, the catalyst particles of relatively small diameters have inevitably been produced and used as a make-up catalyst, and thus it has been considered inevitable that the amount of the particles to be scattered and lost will increase during the use thereof.
Also a process for production of an antimony oxide-containing fluidized bed catalyst has been proposed as described in Japanese Patent Application (OPI) No. 40288/1974, for useful utilization of coarse catalyst particles formed on use of the catalyst. In accordance with this process, the coarse catalyst is pulverized to particles of a diameter of 20 .mu. or less, and the pulverized catalyst is incorporated into the slurry at an appropriate step prior to the spray-drying according to the method disclosed in U.S. Pat. No. 3,657,155 so that the pulverized catalyst constitutes not more than 50% by weight of the total catalyst weight.
This method of producing catalysts can be utilized as a method of producing catalyst for controlling the particle diameter. Thus, it is possible to produce a catalyst of the desired particle size distribution by removing extremely fine particles and/or coarse particles unsuitable for practical use. However, since the catalyst removed has been calcined at elevated temperatures and has a high strength, the pulverization thereof requires a great deal of energy. In addition, at the time of the spray-drying of the slurry with the catalyst incorporated therein, pieces of apparatus such as a slurry pump, nozzles and the like are subject to a high degree of abrasion and frequent change of parts is needed. Furthermore, in the case, the amount of the pulverized catalyst which can be incorporated is limited; that is, if the pulverized catalyst is added in an amount above 50% by weight, the strength of the final catalyst markedly decreases and thus the final catalyst becomes unsuitable for practical use.